A phylogentic study of structure, function and innervation of the cardiac conduction system in birds (pigeon) and mammals (ferret, mini pig, dog and man). Newborn and adult animals are included to provide developmental information that may be pertinent to human cardiac anomalies, arrhythmias, cardiac innervation and related pathology. Histologic, neurologic, histochemical and fluorescent stain procedures are used in serial section studies to elucidate cellular arrangements and innervation of specific atrial regions (SA and AV nodes, internodal pathways). The same atrial regions of human necropsy hearts are examined in serial section with the light microscope from selected autoposy cases that had demonstrated antemortem cardia arrhythmias followed by sudden or unexplained death (SUD). BIBLIOGRAPHIC REFERENCES: R.C. Truex, Sinoatrial Node and its Connections with the Atrial Tissues. In: Conduction System of the Heart. Ed. H.J.J. Wellens. H.E. Stenfert Kroese B.V./Leiden. 1976. Pages 207-226.